1. Field of the Invention
The present invention relates to a waste water treatment method and apparatus which utilizes silicon sludge obtained from silicon waster water, discharged from for example a semiconductor factory, for treating fluorine waster water in a separate waster water treatment system.
2. Description of the Related Art
In a semiconductor factory, after a silicon wafer is polished, it is cleaned with water. Thus, the factory has silicon waste water containing silicon particles.
Treated water derived from the silicon waste water, from which the silicon particles have been separated, has a high quality. Therefore, the treated water is discharged from the factory without being subjected to a further treatment or recycled as the raw water to be treated in an ultrapure water system.
On the other hand, the separated silicon particles exist in an aggregated form of sludge. The silicon sludge is dehydrated by a dehydrator and then disposed of, for example, as landfill, outside the semiconductor factory.
Japanese Patent Publication No. 2720830 discloses that silicon particles are recovered from a suspension which is a silicon particle-suspended calcium hydroxide solution, and that the recovered silicon particles are mixed with activated sludge to increase the settling performance of the activated sludge.
On the other hand, to treat fluorine waste water, hitherto, a calcium agent such as calcium hydroxide or calcium carbonate mineral is added or loaded to the waste water to chemically react fluorine contained in the waste water with calcium of the calcium agent, using a stirring means such as a stirrer or pneumatic stirring.
Conventionally, such stirring means has been infallibly used to cause a neutralization reaction of waste water and a chemical reaction of fluorine in the waste water. In those days not requiring complete implementation of energy-saving measures, however, the cost for electricity consumed by the stirring means was not regarded as important.
A conventional waste water treatment method is shown in FIG. 1B. In the conventional method, acid waste water is introduced into a neutralization tank 46 from an introduction tank 1 by a pump 2 and an alkali agent such as caustic soda is added to the waste water there. Then, the acid waste water loaded with the alkali agent is stirred by a rapid stirrer 18 to get neutralized.
FIG. 1C shows another conventional waste water treatment method. In FIG. 1C, parts similar to the parts shown in FIG. 1B are denoted by the same reference numerals. In the conventional method shown in FIG. 1C, acid waste water is pumped into a neutralization tank 46 from an introduction tank 1 by a pump 2. An alkali agent such as caustic soda is added to the acid waste water, and air generated by a blower 14 is discharged from an air-diffusing pipe 22 to neutralize the acid waste water by pneumatic stirring.
Returning to the treatment of fluorine waste water, fluorine waste water discharged from the semiconductor factory contains not only hydrofluoric acid which is a main component of the fluorine waste water but also nitric acid, ammonia water, phosphoric acid, hydrogen peroxide, and organic matters including a surfactant. Thus, it is necessary to also treat the latter components.
It is reported that a part of the surfactant may become an environmental hormone. Thus, reliable treatment is demanded.
Nitrogen and phosphorous resulting from the nitric acid, the ammonia water, and the phosphoric acid are considered to be substances causing eutrophication. Thus, it is necessary to treat nitrogen and phosphorus from the viewpoint of preventing red tide that is generated on the sea. In ordinary denitrifying equipment and phosphorus-removing equipment, however, the initial cost and the running cost are high.
In recent years, the pollution of ground water caused by an organic chlorine compound, or organic chloride, discharged from existing factories has been taken up as a serious problem. According to an ordinary method, the ground water containing the organic chloride is drawn up and aerated so that the vaporized organic chloride is adsorbed to activated charcoal. There is known another method in which the organic chloride is decomposed by being irradiated with ultraviolet light. According to another known method, the organic chloride is dechlorinated by its contact with a metal surface. According to still another known method, it is treated by microorganisms (bio-remediation).
Still another conventional method of treating the organic chloride is disclosed in Japanese Patent Application Laid-Open No. 10-113679. In the conventional method, silicon is added to a polluted environment to accelerate dechlorination reaction of the organic chlorides (contaminant), such as carbon tetrachloride, tetrachloroethylene, and the like, to thereby decompose it.
Examples of the conventional waste water treatment methods will be described below in more detail with reference to FIGS. 19 and 20 in which parts similar to the parts shown in FIGS. 1B and 1C are denoted by the same reference numerals.
In a first example of treating silicon waste water shown in FIG. 19, silicon and treated water are separated from each other by a coagulation and settlement method, and the treated water is utilized as raw water in an ultrapure water system.
In the method of treating silicon waste water shown in FIG. 19, silicon waste water is introduced into a storage tank 30 and stored therein and then fed to a reaction tank 32 by a storage tank pump 31. Polychlorinated aluminum (not shown) serving as a flocculating agent and caustic soda (not shown) serving as a neutralization agent are loaded into the reaction tank 32 to form flocs containing silicon 42. The silicon flocs are introduced into a settling tank 33 in which the flocs are separated into silicon as a solid matter and treated water as a supernatant liquid.
The treated water, supernatant, is introduced into a storage tank 37. Then, by a high-pressure pump 38, the treated water is fed to a prefilter 39, then to a reverse osmosis membrane device 40, and finally to a ultrapure water system 41 in which the water is utilized as raw water. On the other hand, the silicon floc that has precipitated in the settling tank 33 becomes silicon sludge. Then, a concentration 44 concentrates the silicon sludge. A filter press pump 45 feeds the concentrated silicon sludge to a filter press 46 for dehydration. After the silicon is dehydrated, it is disposed of as landfill, without being recycled, as described above. The disposal by landfill has been a typical method.
Fluorine waste water is treated by a different waste water treatment system. Fluorine waste water is introduced into an introduction tank 1 and then fed to a calcium hydroxide tank 17 by an introduction tank pump 2. Calcium hydroxide is added to the fluorine waste water contained in the calcium hydroxide tank 17 in which a rapid stirrer 18 stirs the fluorine waste water and the calcium hydroxide to mix and react them with each other. That is, calcium ions of the calcium hydroxide and fluorine contained in the fluorine waste water react with each other to form fine and refractory particles of calcium fluoride. The fine particles of calcium fluoride formed in the calcium hydroxide tank 17 are introduced into a polychlorinated aluminum tank 19 in which polychlorinated aluminum serving as a flocculating agent is added to the calcium fluoride to form flocs. Then, the flocs are introduced into a macromolecular flocculant tank 21 in which a macromolecular flocculant is added to the flocs to form larger stable flocs. Those flocs are introduced into a settling tank 23 in which the flocs are separated into a supernatant liquid and a precipitated matter, or sludge. The treated water, or the supernatant liquid, is discharged outside. The calcium fluoride sludge obtained as the precipitated matter is introduced into a concentration tank 26 and concentrated. Finally, the concentrated calcium fluoride sludge is fed to filter presses 29a and 29b by respective concentration tank pumps 28a and 28b for dehydration. The dehydrated sludge is disposed of by landfill.
The problem inherent in the above method for treating the fluorine waste water is that the concentrated sludge in the concentration tank 26 contain a lot of unreacted chemicals of calcium hydroxide, polychlorinated aluminum, and macromolecular flocculent so that the treatment of the sludge tends to fall into arrears unless two filter presses 29a and 29b are used for dehydration, as shown in FIG. 19.
The reason the concentrated sludge contains the unreacted chemical agents is that unless a large amount of chemical agents is used in the calcium hydroxide tank 17, the polychlorinated aluminum tank 19, and the macromolecular flocculent tank 21, the fluorine concentration of the treated water, namely, the supernatant liquid in the settling tank 23, does not drop to a predetermined value. Therefore, to maintain the quality of the treated water, a large amount of the chemical agents has been used so far.
Factories know the above fact experimentally and do not regard it as serious as far as the quality of the treated water is maintained. But nowadays, reducing the amount of waste is an evaluating point of an enterprise. Accordingly, it is necessary to improve the waste water treatment system in view of the reduction of waste and effective utilization of resources.
A second example of a conventional method of treating waste water shown in FIG. 20 is described in detail below. Similarly to the first example, in the second example, the silicon waste water and the fluorine waste water are separately treated, but the second example is different from the first example in the way of treating the silicon waste water. According to the second conventional method, silicon and treated water are separated from each other by a membrane separation method, and the treated water is utilized as the raw water in the ultrapure water system.
That is, in the second conventional example, the silicon waste water is introduced into a storage tank 30 and stored therein, and then, fed to a membrane separator 47 by a storage tank pump 31. The membrane separator 47 separates the silicon waste water into silicon and treated water securely. The separated treated water is introduced into a storage tank 37. Then, by a high-pressure pump 38, the treated water is fed to a prefilter 39, then to a reverse osmosis membrane device 40, and finally to a ultrapure water system 41 in which the water is utilized as raw water. On the other hand, the silicon-containing water that has not passed through the membrane is concentrated by a concentrator 44. A filter press pump 45 feeds silicon sludge resulting from the concentration to a filter press 46 by which the silicon sludge is dehydrated. Thus, according to the second example as well, the dehydrated silicon is disposed of by landfill without being recycled.
As described above, stirring means such as the stirrer and the pneumatic stirrer are required for neutralization and chemical reactions in the conventional waste water treatment methods. A power (electric power) is necessary for driving the stirring means.
Therefore, if the neutralization and chemical reactions can be accomplished without using the stirring means, saving of energy can be achieved. The saving of energy will be especially important in factories such as semiconductor factories and liquid crystal factories which generate large amounts of waste water and thus require large amounts of electricity to drive the stirring means and the blower, indispensable for the neutralization and chemical reactions but at high cost.
In the Kyoto conference on global warming (COP3: Third Session of the Conference of the Parties to the United Nations Framework Convention on Climate Change), attendants agreed to make positive energy-saving efforts. Implementation of energy saving is demanded in all kinds of equipment. An energy-saving waste water treatment method which does not require the use of the stirring means is also demanded in the field of waste water treatment.
Nowadays, recycling of resources is an important theme. The silicon sludge derived from the silicon waste water generated in the semiconductor factory is effective for increasing the settling performance, or sedimentation property, of activated sludge derived from domestic waste water or the like. Therefore, utilization of the silicon sludge as the settling agent of the activated sludge is conceivable.
However, in the semiconductor factories, the scale of the existing waste water treatment equipment utilizing the activated sludge is not large enough to recycle the silicon sludge sufficiently. To utilize the silicon sludge generated in the semiconductor factories for factories of different fields, it is necessary to transport the silicon sludge, which incurs costs.
Accordingly, it would be advantageous to utilize the silicon sludge generated in a waste water treatment system of a semiconductor factory for a different waste water treatment system of the same factory. It would also be advantageous to utilize acid waste water and alkali waste water effectively in addition to the silicon waste water.
As described above, in the conventional fluorine waste water treatment methods, experimentally, treated water having an intended quality cannot be obtained without using a large amount of calcium agent such as calcium hydroxide and a large amount of flocculating agent. Thus, sludge generated in the conventional fluorine waste water treatment process contains unreacted calcium hydroxide and unreacted flocculating agent. This is not rational from the viewpoint of effective utilization of resources. Accordingly, there is a demand for the development of a waste water treatment system which can utilize the calcium hydroxide and the flocculating agent effectively and completely.
Further, it would be a great convenience if a fluorine waste water treatment system can treat both fluorine waste water and ground water containing organic chlorides of topical interest. In this case, it is unnecessary to install new equipment, which is rational.
In the waste water treatment method which is disclosed in Japanese Patent Application Laid-Open No. 10-11369, to treat organic chlorides (polluting substance) such as, for example, carbon tetrachloride and tetrachloroethylene, silicon is added to a polluted environment to accelerate the dechlorination reaction of the organic chlorides to thereby decompose them. That is, this method requires the addition of silicon to the polluted environment. But, if the polluted environment is soil, it is difficult to permeate silicon into the entire polluted environment. Further, if the soil is large, it is necessary to use a large amount of silicon. Thus, this method is not a practical method.
Therefore, an object of the present invention is to provide a waste water treatment method and apparatus which can reduce electric power consumption and the amount of chemical agents needed as much as possible to achieve savings of energy and effectively utilize resources.
In order to accomplish the object, a waste water treatment method according to an aspect of the present invention neutralizes acid waste water with alkali sludge without using stirring power.
In this waste water treatment method, the acid waste water is neutralized with the alkali sludge. Neutralization treatment is generally considered to be a treatment of the acid waste water by adding an alkali agent thereto and stirring it. However, neutralization of the acid waste water can be also accomplished, without using a stirring power, by introducing the acid waste water into a tank in which a great deal of alkali sludge is present.
In the case where the alkali sludge contains unreacted chemical agent (calcium hydroxide or the like), the acid waste water is neutralized by the chemical agent. Thereby, the unreacted chemical agent is recycled. Because normally, a residence (reaction) time period is short in a reaction tank, unreacted chemical agent is necessarily contained in the sludge.
When the acid waste water is fluorine waste water, and the unreacted chemical agent is a calcium agent, fluorine in the fluorine waste water and calcium in the calcium agent chemically react with each other to form calcium fluoride. In this manner, fluorine in the waste water is treated.
If the calcium agent comprises calcium hydroxide, a waste water treatment system can be easily constructed. Further, calcium reacts with fluorine smoothly in solution if calcium derived from calcium hydroxide is used. In this connection, other calcium compounds such as CaCO3 exist as large grains or lumps like stones and thus are hardly soluble. To contrast, because the calcium hydroxide is powdery, it is soluble.
In the case where the unreacted chemical agent comprises a flocculating agent in addition to the calcium hydroxide, the flocculating agent flocculates fine particles of calcium fluoride, which has been formed by the reaction of the fluorine contained in the fluorine waste water and the calcium of the calcium hydroxide, into large flocs.
If polychlorinated aluminum, aluminum sulfate (sulfuric acid band) or macromolecular flocculant is used as the flocculating agent, a waste water treatment system can be easily designed or constructed. The macromolecular flocculant can make large flocs larger and stable.
If return sludge is used as the alkali sludge for neutralizing the acid waste water, it is easy to secure the alkali sludge in the waste water treatment system. Further, it is unnecessary to obtain the alkali sludge from different waste water treatment equipment. Further, the return sludge is not so expensive as a chemical agent is.
In the case where the alkali sludge contains silicon, it is possible to form sludge that is firm and settles favorably even though the alkali sludge is light and fluffy.
Japanese Patent Publication No. 2720830 teaches how to accelerate the settling performance of activated sludge in a fluidized state by utilizing silicon. In contrast, utilization of silicon according to the present invention is intended to change stationary sludge into strong and firm sludge (change only the property of the stationary sludge). Thus, the present invention is fundamentally different from the content of this patent publication. That is, use of silicon according to the Japanese Patent Publication No. 2720830 is intended to enhance the settling performance of the activated sludge, whereas use of silicon according to the present invention is intended to allow a sludge zone to be strong and firm, in addition to the enhancement of the settling performance of the sludge. Because silicon is heavy, it is possible to proceed neutralization and reaction reliably by introducing the acid waste water little by little into a lower portion of the strong and firm sludge zone.
In a waste water treatment apparatus according to another aspect of the present invention, waste water is treated in a main treatment tank into which return sludge and silicon sludge are introduced from an upper portion thereof and fluorine waste water is introduced from a lower portion thereof. That is, the direction in which the return sludge and the silicon sludge are introduced is opposite to the direction in which the fluorine waste water is introduced. Further, the return sludge and the silicon sludge contain a large amount of a solid matter, respectively. Accordingly, the fluorine waste water does not pass the main treatment tank in a short period of time and thus reaction can proceed reliably.
Recycling of silicon can be achieved by utilizing silicon sludge coming from a different waste water treatment system in which the silicon sludge is obtained by subjecting silicon waste water to either a coagulation and settling process or a membrane separation process.
In one embodiment, the waste water treatment apparatus comprises an introduction tank in which fluorine waste water is mixed with ground water containing an organic chloride, and the mixture is introduced into the main tank.
In this case, silicon metal contained in the silicon sludge acts on the organic chlorine compound or chloride contained in the ground water to dechlorinate the organic chloride for decomposition. Also, unreacted chemical agents contained in the return sludge treat fluorine contained in the waste water.
The silicon sludge to be introduced into the main tank may be silicon sludge obtained by treating silicon waste water by either a coagulation and settlement device having a magnet or a membrane separator having a magnet.
Because of the magnet, neither the coagulation and settlement device nor the membrane separator will hardly clog even if the silicon sludge concentration becomes high. Accordingly, reliability of the waste water treatment system can be improved.
In this connection, passage of the sludge through a magnetic field generated by the magnet prevents a pipe or the like of the waste water treatment apparatus from being clogged with the sludge and thus from becoming scaly. The magnet used in the waste water treatment apparatus may be a permanent magnet having a high intensity. Then, Si (silica) is ionized and thus the solidified silicon sludge can be decomposed.
The membrane separator may be constructed of a ultrafiltration membrane so that a waste water treatment system can be easily constructed. Silicon particles having a diameter of more than 0.5 microns can be separated by selecting a ultrafiltration membrane having a pore diameter of 0.5 microns. Many types of ultrafiltration membranes commercially available have a pore diameter of 0.5 microns.
The present invention also provides a waste water treatment apparatus, comprising:
an introduction tank into which fluorine waste water is introduced;
a main treatment tank having an upper part into which return sludge fed from a settling tank and silicon sludge fed from a different waste water treatment system are introduced and a lower part into which the fluorine waste water is introduced from the introduction tank;
a calcium hydroxide tank into which waste water is introduced from the main treatment tank and in which calcium hydroxide is added to the waste water;
a polychlorinated aluminum tank into which waste water is introduced from the calcium hydroxide tank and in which polychlorinated aluminum is added to the waste water;
a macromolecular flocculant tank into which waste water is introduced from the polychlorinated aluminum tank and in which a macromolecular flocculant is added to the waste water; and
the settling tank into which waste water is introduced from the macromolecular flocculant tank and in which the waste water is separated into solid and liquid components.
In this waste water treatment apparatus, initially, calcium of unreacted calcium hydroxide reacts with fluorine in the fluorine waste water to form calcium fluoride (primary treatment of fluorine) in the main treatment tank. Secondly, in the calcium hydroxide tank, calcium hydroxide is added to the waste water to react with the fluorine remaining in the waste water into calcium fluoride (secondary treatment of fluorine). Then, in the polychlorinated aluminum tank, polychlorinated aluminum is added to the waste water to flocculate particles of calcium fluoride formed by the secondary treatment into flocs. Then, in the macromolecular flocculant tank, the macromolecular flocculant is added to the waste water to enlarge the flocs such that the flocs can settle easily. Then, the waste water being treated is introduced into the settling tank to be separated into solid and liquid components. Due to the improved settling property of the flocs, sludge that settles and the supernatant liquid can be reliably separated from each other. In this manner, fluorine contained in the waste water is treated securely and thus treated water is stably obtained.
The present invention also provides a waste water treatment apparatus, comprising:
an introduction tank into which fluorine waste water is introduced;
a main treatment tank having an upper part into which return sludge fed from a concentration tank and silicon sludge fed from a different waste water treatment system are introduced and a lower part into which the fluorine waste water is introduced from the introduction tank;
a calcium hydroxide tank into which waste water is introduced from the main treatment tank and in which calcium hydroxide is added to the waste water;
a polychlorinated aluminum tank into which waste water is introduced from the calcium hydroxide tank and in which polychlorinated aluminum is added to the waste water;
a macromolecular flocculant tank into which waste water is introduced from the polychlorinated aluminum tank and in which a macromolecular flocculant is added to the waste water;
a settling tank into which waste water is introduced from the macromolecular flocculant tank and in which the waste water is separated into solid and liquid components; and
the concentration tank for concentrating settled sludge fed from the settling tank.
In this apparatus, both return sludge from the concentration tank and silicon sludge from the waste water treatment equipment of a different line are introduced into the upper part of the main treatment tank. Accordingly, as compared with the case in which return sludge comes from the settling tank, a firmer sludge zone is formed in the main treatment tank. Thus, reliable treatment can be accomplished.
The return sludge may be fed both from the concentration tank and the settling tank to the main treatment tank. In this case, much sludge is returned to the main treatment tank. Thus, the fluorine waste water can be treated even when the waste water has a very high concentration or the amount thereof is large.
The present invention also provides a waste water treatment apparatus comprising:
an anaerobic tank which contains a calcium carbonate mineral and has a separation part for separating the calcium carbonate mineral and treated water from each other an into which return sludge is introduced; and
and aerobic tank which contains a calcium carbonate mineral and has a separation part for separating the calcium carbonate mineral and treated water from each other and into which silicon sludge and return sludge are introduced, and wherein
fluorine waste water containing an organic matter, nitrogen, phosphorus, and/or hydrogen peroxide is treated by the anaerobic tank and the aerobic tank.
In the apparatus, fluorine contained in waste water is treated by the calcium carbonate mineral in the anaerobic tank and the aerobic tank, and organic matters contained in the waste water are biologically treated to be degraded by microorganisms that propagate in the anaerobic tank and the aerobic tank. The anaerobic tank and the aerobic tank have their respective separation parts. Thus, the calcium carbonate mineral, which has a high specific gravity, does not flow out from the anaerobic tank and the aerobic tank.
In the anaerobic tank, components contained in the return sludge react with the waste water. On the other hand, in the aerobic tank, because not only return sludge but also the silicon sludge is introduced, the sludge in the tank is heavy and firm. Thus, while the waste water is passing through the firm sludge, the components of the sludge and the components of the waste water react with each other slowly. In the anaerobic tank, hydrogen peroxide contained in the waste water is treated.
The fluorine waste water is treated in two stages by microorganisms in the anaerobic tank and in the aerobic tank. Therefore, the apparatus of the present invention is able to treat even fluorine waste water containing a hardly biodegradable surfactant.
Because in the apparatus, the sludge zone is formed in the anaerobic tank and the aerobic tank, the concentration of the sludge is high. Thus, treatment can efficiently proceed.
The present invention also provides a waste water treatment apparatus, comprising:
an anaerobic tank having an upper part providing an anaerobic sludge zone and a lower part filled with calcium carbonate mineral; and
an aerobic tank which has an upper part constituting an aerobic sludge zone and a lower part filled with a calcium carbonate mineral and into which silicon sludge and returned sludge are introduced, and wherein
fluorine waste water containing an organic matter, nitrogen, phosphorus, and hydrogen peroxide is treated by the anaerobic tank and aerobic tank.
In one embodiment, sludge of the anaerobic sludge zone at the upper part of the anaerobic tank contains unreacted calcium hydroxide, unreacted polychlorinated aluminum, an unreacted macromolecular flocculent, generated calcium fluoride, and microorganisms. Similarly, sludge of the aerobic sludge zone at the upper part of the aerobic tank contains unreacted calcium hydroxide, unreacted polychlorinated aluminum, an unreacted macromolecular flocculant, generated calcium fluoride, and microorganisms.
Because the sludge zone is formed both in the anaerobic tank and in the aerobic tank, the sludge concentration is high. Thus, treatment can proceed efficiently.
Phosphorus contained in the waste water is formed into fine particles of calcium phosphate by the chemical reaction with unreacted calcium hydroxide. Further, the unreacted polychlorinated aluminum and the unreacted macromolecular flocculent turn the fine particles of calcium phosphate to large flocs.
Further, because the sludge of the anaerobic sludge zone contains generated calcium fluoride, anaerobic microorganisms propagate by using the calcium fluoride as a fixing carrier on which the microorganisms are fixed. Accordingly, hydrogen peroxide in the waste water can be efficiently treated.
In the aerobic tank, a slight amount of fluorine contained in the waste water is turned to calcium fluoride by the reaction with calcium hydroxide, and phosphorus is treated as calcium phosphate. Further, organic matters are treated by aerobic microorganisms. Furthermore, because aerobic microorganisms are present in the aerobic sludge zone, ammoniacal nitrogen and nitrite nitrogen are oxidized to nitrate nitrogen.
For the purpose of denitrification, the fluorine waste water is introduced into the anaerobic tank first and then to the aerobic tank. Nitrate nitrogen contained in the waste water can be treated as nitrogen gas by anaerobic microorganisms that propagate in the anaerobic sludge zone of the anaerobic tank, and using an organic matter in the waste water as a hydrogen donor. Because the microorganisms in the aerobic sludge zone of the aerobic tank is aerobic, ammoniacal nitrogen and nitrite nitrogen contained in the waste water can be oxidized to nitrate nitrogen. The ammoniacal nitrogen and nitrite nitrogen will be returned to the anaerobic tank to be finally treated as nitrogen gas. In this way denitrification is achieved.
The present invention further provides a waste water treatment apparatus comprising:
an introduction tank into which fluorine waste water containing an organic matter, nitrogen, phosphorus, and/or hydrogen peroxide is introduced;
an anaerobic tank containing calcium carbonate mineral, into which waste water from the introduction tank and return sludge are introduced;
an aerobic tank having a stirring means and containing a calcium carbonate mineral, into which waste water from the introduction tank, return sludge, and silicon sludge are introduced, the waste water being mixed with the return sludge and the silicon sludge;
a calcium hydroxide tank into which waste water is introduced from the aerobic tank and in which calcium hydroxide is added to the waste water;
a polychlorinated aluminum tank into which waste water is introduced from the calcium hydroxide tank and in which polychlorinated aluminum is added to the waste water;
a macromolecular flocculent tank into which waste water is introduced from the polychlorinated aluminum tank and in which a macromolecular flocculant is added to the waste water;
a settling tank into which waste water is introduced from the macromolecular flocculant tank; and
a concentration tank into which a precipitated matter in the settling tank is introduced.
In one embodiment, treated water at an upper part of the settling tank is returned to an intermediate part of the anaerobic tank. In this case, nitrate nitrogen contained in the treated water in the upper part of the settling tank is removed by denitrifying microorganisms in the upper part of the anaerobic tank.
In one embodiment, ground water containing a organic chlorine compound is introduced into the introduction tank and mixed with fluorine waste water containing an organic matter, nitrogen, phosphorus, and/or hydrogen peroxide. Therefore, it is possible to treat various components, namely, the organic chlorine compound, the organic matter, the nitrogen, the phosphorus, and/or the hydrogen peroxide contained in the waste water. The organic chlorine compound is treated by the dechlorination action of silicon contained in silicon sludge introduced into the aerobic tank.